Electrical discharge control and television system



Dec. 8, 1936.

H. c. GILLESPIE 2,063,804

ELECTRICAL DISCHARGE CONTROL AND TELEVISION SYSTEM Filed June 21, 1933 AMP.

' Per/'00 of /'//um/'naf/bn Per/lad Of of one uni? area carrier fre TH I, Dark Brighf CURRENT TIME INVENTOR ATTORNEY Patented Dec. 8, 1936 ELECTRICAL DISCHARGE CONTROL, AND

TELEVISION SYSTEM 1 Henderson 0. Gillespie, New York, N. Y., assignor' to Communication Patents, Inc., New York, N. Y., a corporation of Delaware Application June 21, 1933, Serial No. 676,826

7 Claims. (01. 178-6) This invention relates to the electro-optical transmission of information from point to point, and particularly to electro-optical transmission known as television, wherein the reproduction of an object in varying intensities of light is at a rate within the persistence of vision. Television systems of various types are well known in the art, such as those employing mechanical scanning arrangements for analyzing an objectinto unit areas by means of an apertured disk or drum, cathode ray systems, crystal screens, shutter screens and electrodynamic' discharge screens, the latter of which are disclosed in Alexander McLean Nicolsons Patents Nos. 1,839,696 and 1,863,278, and my co-pending United States application Serial No. 584,797, filed January 5, 1932. These electrical discharge systems employ an electrical discharge or are propagated along electrode "rails, the light from which is projected in a unit area beam for scanning an object or image thereof.- The reflected or energized light is detected by a photo sensitive device and is transmitted to a similar are screen for reproduction. The are screen disclosed in the above-mentioned patents and copending application employs continuous electrodes along which the arc' is propagated, the

speed of the are being controlled by synchronizing impulses, variations in the field or a feedback arrangement which causes the transmitter arc to follow the variations in speed of the receiving arc. I

Thepresent invention is directed to a new and novel construction of the are screen with a particular' energy supply to provide not only very stable propagation of the arc'or discharge, buta flexible and accurate speed control at higher rates than previously possible. 7

, An'object of the invention is to accomplish television with transmitting and receiving apparatuscontaining no mechanical moving elements whatsoever.

Another object of the invention is to improve the speed controlof an electric discharge moving under the influence of a magnetic field.

Another object of the invention is to stabilize the operation of a moving electrical discharge and cause it to travel at higher speeds than has heretofore been possible. V

In developing speed control of an electrical discharge in the above-mentioned electrodynamic systems it'was found that when an are or discharge was created and extinguished, the ions produced did not immediately recombine into neutral'atoms and molecules, but remained in their active state so that the arc would strike at a lower voltage and at a point where the ions existed. Furthermore, it was found thatif the magnetic field was acting during the entire period of light and darkness, the ions would be so acted upon that the arc would actually strike at a point slightly beyond where it' was extinguished. Upon these facts, arc screens were constructed which had rails with protuberances therefrom spaced 1 at uniform intervals and screens with rails of a saw-tooth design. When an alternating or unipotential voltage, was applied to such a screen it was found that the arc was propagated along the rails or gaps by being struck and extinguished from point to point. Also, that the arc current or intensity could be varied considerably without changing the speed of propagation, while the speed of propagation was varied with a change in frequency of the alternating component applied. that higher speeds of the arc could be obtained in this manner than were heretofore obtainable with the smooth continuous type of electrode rails,.although just why this was brought about is not understood.

g The invention, however, will be more fully understood from the following description read in conjunction with the accompanying drawing in which:

Fig. 1 is a diagrammatic drawing of a television transmitter embodying the invention;

Fig. 2 is a similar drawing of the conjugate receiver for the transmitter of Fig. 1, and;

Fig. 3 is a graph showing the arc currents in the receiving screen. 7

Referring to Fig. l in particular, a television scanning screen 5. includes continuous are rails 6 and l in saw-tooth form, a mask 8 to hide the turning points, and a field winding 9, the field winding actually consisting of a plurality of turns for producing a flux perpendicular to the are created between the electrode rails. The field is supplied from a direct current source l2 under control of a rheostat I3. The arcrails are supplied froma vacuum tube amplifier l having a plate potential source I 6 and a cathode heating supply ll. The amplifier l5 has connected in its input circuit a source of alternating current l8, variable in frequency. The tube I5, therefore, supplies electrodes 6 and l with direct current having an alternating'current component.

Positioned anteriorly of the screen 5 is an aperture plate 20 to produce a unit area light beam for projection on anobject 0, shown as Q;

Furthermore, V

an arrow. Light from the object is detected by a photoelectric cell 2i and the currents or voltages generated are fed into an amplifier 22, from whence they are impressed upon a modulator 23, supplied from a carrier frequency source 2d. The output of the modulator 23 may be impressed upon an antenna 25 for transmission by wireless or upon a wire transmission line.

Referring back to the television screen 5, the electrode rails are shown in saw-tooth form with projecting points substantially opposite one another, the arc being formed between opposite points by the peak of each alternating current component. These series of gaps may be constructed in any manner as long as they are at substantially equal intervals. The tips may also be round as well as pointed. The ions formed by the striking of the are are moved along the path of the electrodes by the magnetic field during the time when the arc is extinguished, as well as when the arc exists and each succeeding arc strikes at succeeding points. The arc will have a general speed dependent upon the strength of the field 9 and the frequency and intensity of the arc current, and may be varied over a considerable range by changes in frequency of the oscillator 58. In the photoelectric cell Zi there will be produced an alternating current wave which varies in intensity or amplitude in accordance with the intensity of each unit area scanned and in periodicity with the propagation of the are. This periodic frequency is transmitted with the carrier wave from the oscillator 2t and is used for synchronizing purposes.

Referring now to Fig. 2, an antenna 38 picks up the electromagnetic waves from the antenna 25 and feeds an amplifier 3i. From an intermediate stage of the amplifier a portion of the energy is impressed upon a detector 32, which after demodulation of the carrier is impressed upon an oscillator 33 to maintain this oscillator in step with the transmitter oscillator, and thereby synchronizing the electrical discharges at the transmitter and receiver. After complete amplification in amplifier 3i, the output is fed onto an arc screen 35, similar to screen 5, through a coupling condenser 33 and a vacuum tube 38. Tube 38 has a plate voltage supply 39 and a cathode heating supply 38. The input of vacuum tube 38 is connected to the oscillator 33 for the purpose of producing across the electrode rails t2 and 53 the same periodic potential variations as occur across electrodes 8 and l at the transmitter, due to oscillator l3. A high frequency choke 3'5 provides a direct current path for tube 38 and prevents a short circuit of amplifier iii. The screen 35 includes a magnetic field winding supplied from a direct current source it under control of a rheostat 41.

The receiver operates by detecting the incoming waves which have been modulated by the currents from photo-electric cell 2! and supplying the output to oscillator 33, to maintain it in step with the oscillator i8, while the undemodulated output of amplifier 3! is impressed directly upon the electrodes of screen 35.

By referring to Fig. 3, where the nature of these currents are shown graphically, a better understanding of the operation of the entire system may be had. The frequency of oscillator I8 is represented by the groups of carrier frequency waves, while the modulation or light intensities ofunit areas of the object are represented by the amplitude of the carrier frequency. That is, each group of carrier frequencies represents the time of the arc at one point or position, there being a time lapse between each group, due to the arc being extinguished while the ions move from one pair of points to the next or from gap to gap. In other words, scanning is by step-by-step propagation, the arc being extinguished during a certain period of the movement. It is to be understood that the arc is naturally bowed by the magnetic field at the time it exists and this movement, together with the force of the field on the ions existing after the arc is extinguished, causes the arc to strike at the succeeding point. Although the arc is created at intervals in steps, the optical system enables the arc to cover the entire field. Also, at the receiver substantially no dark areas are apparent by direct observation. By using harmonics of the frequency, two arcs have been made to form at one point and even as high as five arcs have been created at a single gap before sufficient ions have been moved to a succeeding gap to cause it to strike at the later point. However, by proportioning the field strength to the direct and alternating current components in the arc, considerable variation in field strength and the direct current componentmay be made before the speed changes. On the other hand, a change in the frequency of the alternating component will control the speed. There is provided, therefore, a very flexible means for controlling the speed of the are, as well as an are system which is stable during modulation of the arc by the incoming signals, or due to fluctuations in an external energy supply.

What is claimed is:

1. An illuminating screen comprising a plurality of corrugated electrodes having parallel axes, means for maintaining a magnetic field in which said electrodes are located, and means for sucessively initiating a series of arcs along said electrodes.

2. An illuminating screen comprising a plurality of rows of electrodes having parallel axes and of alternate polarity, means for creating a local field around said electrodes, said electrodes having foreshortened gaps at substantially equal intervals, and means for impressing a varying potential on said electrodes to create a series of electrical discharges along said gaps.

3. In a television system a plurality of illuminating screens each having a plurality of spaced electrodes having parallel axes, said electrodes having foreshortened gaps at substantially equal intervals along the length thereof, each of said intervals being of the dimension of a unit area of the picture, and respective oscillators producing a series of discharges along said electrodes at said gaps, one of said oscillators controlling the frequency of the output of the other oscillators.

4. An illuminating screen for picture transmission comprising a plurality of spaced electrodes having parallel axes, said electrodes having foreshortened gaps at substantially equal intervals along the length thereof, said interval being of the order of the dimension of a unit area of the picture, and means for establishing a discharge between the electrodes.

5. An illuminating screen for picture transmission comprising a plurality of spaced electrodes having parallel axes, said electrodes having ioreshortened gaps at substantially equal intervals along the length thereof, said interval being of the order of the dimension of a unit area of the picture, means including a source of alternating current for establishing periodic discharges between said electrodes, and means for producing a magnetic field for propagating said discharge along said electrodes.

6. An illuminating screen comprising a plurality of electrodes having their axes equally spaced from one another and having projections therefrom at substantially equal intervals along the length thereof, said projections being arranged to form a coordinate picture area, and means for creating a series of electrical discharges between said electrodes at successive intervals, each discharge being of the order of the dimension of a unit area of the picture.

7. An illuminating screen for picture transmission comprising a plurality of electrodes havtheir axes parallel and equally spaced, said electrodes having foreshcrtened gaps at substantially equal intervals along the length thereof, said interval being of the order of the dimension of a unit area of the picture, and means for establishing a discharge between said electrodes.

HENDERSON C. GILLESPIE. 

